1. Field of the Invention
The present invention relates to a sample separating apparatus and method, and a substrate manufacturing method and, more particularly, to a separating method and apparatus for separating a plate-like sample having a separation layer at the separation layer, and a substrate manufacturing method using the method and apparatus.
2. Description of the Related Art
A substrate (SOI substrate) having an SOI (Silicon On Insulator) structure is known as a substrate having a single-crystal Si layer on an insulating layer. A device using this SOI substrate has many advantages that cannot be achieved by ordinary Si substrates. Examples of the advantages are as follows.
(1) The integration degree can be increased because dielectric isolation is easy.
(2) The radiation resistance can be increased.
(3) The operating speed of the device can be increased because the stray capacitance is small.
(4) No well step is necessary.
(5) Latch-up can be prevented.
(6) A complete depletion type field effect transistor can be formed by thin film formation.
Since an SOI structure has the above various advantages, researches have been made on its formation method for several decades.
As one SOI technology, the SOS (Silicon On Sapphire) technology by which Si is heteroepitaxially grown on a single-crystal sapphire substrate by CVD (Chemical Vapor Deposition) has been known for a long time. This SOS technology once earned a reputation as the most matured SOI technology. However, the SOS technology has not been put into practical use to date because, e.g., a large amount of crystal defects are produced by lattice mismatch in the interface between the Si layer and the underlying sapphire substrate, aluminum that forms the sapphire substrate mixes in the Si layer, the substrate is expensive, and it is difficult to obtain a large area.
Various SOI technologies have appeared next to the SOS technology. For these SOI technologies, various methods have been examined to reduce crystal defects or manufacturing cost. The methods include a method of ion-implanting oxygen into a substrate to form a buried oxide layer, a method of bonding two wafers via an oxide film and polishing or etching one wafer to leave a thin single-crystal Si layer on the oxide film, and a method of ion-implanting hydrogen to a predetermined depth from the surface of an Si substrate having an oxide film, bonding the substrate to another substrate, leaving a thin single-crystal Si layer on the oxide film by heating or the like, and peeling one (the other substrate) of the bonded substrates.
The present applicant has disclosed a new SOI technology in Japanese Patent Laid-Open No. 5-21338. In this technology, a first substrate prepared by forming an unporous single-crystal layer (including a single-crystal Si layer) on a single-crystal semiconductor substrate having a porous layer is bonded to a second substrate via an insulating layer. After this, the substrates are separated at the porous layer, thereby transferring the unporous single-crystal layer to the second substrate. This technique is advantageous because the film thickness uniformity of the SOI layer is good, the crystal defect density in the SOI layer can be decreased, the surface planarity of the SOI layer is good, no expensive manufacturing apparatus with special specifications is required, and SOI substrates having about several hundred Å to 10-μm thick SOI films can be manufactured by a single manufacturing apparatus.
The present applicant has also disclosed a technique in Japanese Patent Laid-Open No. 7-302889, in which first and second substrates are bonded, the first substrate is separated from the second substrate without being broken, the surface of the separated first substrate is planarized, a porous layer is formed again, and the porous layer is reused. Since the first substrate is not wasted, this technique is advantageous in greatly reducing the manufacturing cost and simplifying the manufacturing process.
In the above technique, when a substrate (to be referred to as a bonded substrate stack hereinafter) obtained by bonding two substrates is to be separated at the porous layer, it is desired to separate the bonded substrate stack with good reproducibility without damaging the substrates.